Leather replacement compositions and process



4, 1956 J. D. c. WILSON u LEA'IQER REPLACEMENT COMPOSITIONS AND PROCESS3 Sheets-Sheet, 1

Filed May 7, 1954 Loy-up of components in composite sheet beforepressing.

A 6 G 0 1 s Compocted composite sheet:

(Substantially impermeable) Stretch in one or two directions Porousfiber-reinforced sheet having R J. Y N 0 w E I. m e m 1 m W W O t N R um M A m M. m m pt 00. g t n d m m w om r f o w 0 00.1 I f n mtO w .m E r0 5 M. Q |0 UnmOJ w mw r O 1 e h C l- S m b m HMO? mm m man "m h 0 SSPswn 0 s t s nu Xb Efi ll lit 1956 J. D c. WILSON n r 2,772,995

LEATHER REPLACEMENT COMPOSITIONS AND PROCESS Filed Ma 7, 1954 sSheets-Sheet. 2

FIG.2

compacted composite sheet Stage B (Substantially impermeable) Step 2.

Immerse in liquid above the softening temperature of binder to swellstructural fibers and extract pore-forming fibers.

Wet Product having integral.

porous surface strata and swollen structural fibers.

Stage C Step 3.

Dry at temperature below softening temperature of binder to shrink or"de- 1 swell"structural fibers.

structural fibers JOSEPH-DURANT COOPER WIL$ON,1I

ATTORNEY Stage D 4, 1956 J. D. c. WILSON u "2,772,995

LEATHER REPLACEMENT COMPOSITIONS AND PROCESS Filed May 7, 1954 3 Sheets-Sheet- "3 Superimposed mats of structural fibers.

FIG.3

Stage A Stage B Partially compacted composite sheet.

|| Step 3 (Substantially impermeable) & Coat upper surface withpore-forming fibers, e. g., from a dispersion of fibers N4 in an inertmedium.

Hot press to compact and press m pareforming fibers 51098 E Compactedcomposite sheet.

(substantially impermeable) Step5 \Step 5A 7 Stretch in one Immerse inhot liquid to swell structural direcmns fibers and extract pore-formingfibers.

Stage F Step'6A Dry at a temp. Extract poreforming bebw m soften fibersing temp.0f the binder.

Porous fiberreinforced polymeric sheet having 'ntegral porous surfacestrata containing no fibers ATTORNEY United States Patent LEATHERREPLACEMENT COMPOSITIONS AND PROCESS Joseph Durant Cooper Wilson H, NewCastle, Del., assrgnor to E. I. du Pont de Nemours and Company,Wilmrngton, Del., a corporation of Delaware Application May 7, 1954,Serial No. 428,356

12 Claims. (Cl. 154-124) This invention relates to leather replacementcompositions and, more particularly, to leather replacement sheetshaving outstanding resistance to fuzzingupon being subjected to scuffingor abrasion.

Patents relating to methods andtechniques of preparing leatherreplacement compositions have been granted to' inventors as far back as1850; and even before that the early stages of the synthetic leatherindustry, the main objective was to simulate the general appearance ofleather. f. i i i i In todays markets, coated fabrics, particularly thevinyl-coated fabrics, are outstanding as leather substitutes in suchapplications as handbags, bookbindings, brief cases, card table covers,luggage, etc; In such applications, the coated fabrics are satisfactorybecause the general appearance of leather is simulated; and the coatedfabrics possess some of the desirable properties of leather. However, ascompared to genuine leather, the coated fabrics lack good tear strength,softness and the ability to breathe or transpire Water vapor and air;and although the coated fabrics are used in such applications as chaircoverings, much is left to be desired, especially with respect to watervapor and air permeability. Up to the present time, leather replacementcompositions have made little or no inroads into the boots, shoes, andgloves markets, mainly because of their inability to breathe in additionto lack of good tear strength and softness. As used hereinafter, theterm breathe, means transpire water vapor and air. k Q

In general, the use of leather replacement compositions in boots, shoes,gloves,;etc., is mainly dependent upon its ability tobreathe, usuallyexpressed in terms of water vapor permeability or leather permeability]?'Physical testson the water vapor permeability of leather indicate thatleather transpires Water vapor about two-thirds as 4,000-20,000 whentested at 23 C. and not greater than 90% relative humidity.

Recently, various techniques and processes have been developed forpreparing leather replacement compositions which not only have theappearance of leather, but are also capable of breathing. Comparisons ofthe leather permeability of these leather replacement comE positionscompared with genuine leather have shown that the leather permeabilityof these compositions in many cases is superior to that of shoe uppersfabricated from genuine leather. Furthermore, the flexibility of theserecently developed techniques provides for tailoring the compositionsfor particular end uses, that is, produces a product having the desiredwater vapor permea: bility, tear strength, softness, etc. These recentlydeveloped processes for preparing leather replacement compositions donot, however, provide products which are satisfactorily resistant tofuzzing upon being subjected to scufiing or abrasion.

An object of the present invention, therefore, is to provide aleatherreplacement composition having outstanding resistance to surfacefuzzing upon being abraded. A still further object is to provide aprocess of preparing such leather replacement compositions. Theforegoing and other objects will more clearly appear hereinafter. p

These objects are accomplished by the present invention which, brieflystated, comprisesforming a fibrous,- substantially Watervapor-impermeable sheet comprising a base stratum of uniformly dispersedstructural fibers, a

, surface stratum of uniformly dispersed soluble. porereadily as freeair. In general terms, shoe upper leather samples having a thicknessof0.0l6"0.l04" havea leather permeability within the range of 2,000-l8,000

7 grams/100 sq. meters/hour when tested accordingjto the I selectingrelatively non-extensible structuralfibers and method of Kanagy andVickers Journal of American Leather Chemists Association 45, 21l-242(April 1950) in an atmosphere of 23 C. and relative, humidity.

Hereinafter, theability of leather replacement compositolerable leatherpermeabilityfor shoe upper leather is about 2,000 grams/' sq;'meters7hour.- Preferably for shoe upper leather, the permeability valueshould be impermeable'composite sheet-by impregnating'a non-- I formingfibers free of structural fibers, said pore-forming fibers beingsolublein a solvent which is a non solvent for the structural fibers, saidstrata being impregnated with thermoplastic, soft, elastomeric'polymeric. binder material to form a composite sheet, treating saidsheet to cause said structural fibers to break away from said binder,anddissolving out the soluble pore-forming fibers, whereby to form awater vapor-permeable sheet of polymeric binder'material having aporoussurface stratum free of structural fibers and a base stratum havingstructural fibers and contiguous channels distributed there-' through. Ii I The term contiguous channels, as applied tothe interconnecting poresformed in the fiber-reinforced strata of the leathe r'replacement sheetsof this invention, means that the channels or pores'are immediatelyadjacent the structural fibers. It should be emphasized that the poresorchannels are not necessarily wholly annular; that is, the structuralfiber is not necessarily entirely broken away from the surroundingbinder polymer. In some cases, for example, a continuous pore orcapillary may spiral around a continuous length of fiber; whereas, onthe other hand, the capillary, formed by the fibersbreaking away fromthe surrounding binder polymer, may take the form of a hairline crackrunning substantially I parallel and immediately ad jacent a structuralfiber.

Any convenientknown expedient fortreating the initial sheetto cause thestructural fibers to break away-from the poylmeric binder materialtoform contiguous channels in th base stratum may be employed. Thus, by

a binderpolymer which is'extensible relative to the structuralfibers,stretching the-resulting sheetin' one or. both directions will serve tobreak the, embedded fibers away from' the binder polymer and formcontiguous channelsin the sheet upon-removal of the stretchingforces,yi. e.,relaxation. Such a process is disclosed and 'claimed inthe copending application of-V. L. Simril; U. s; Serial No. 318,732,filed November 4,. 1 952. The

processcomprises forming a substantially water .vaporwoven sheet offibers of substantially water vaporirnpermeable, substantiallynon-extensible material with substantially water vapor-impermeable,relatively extensible binder polymer, said binder polymer constitutingfrom about 30% to about 70% by'weight of the total weight of fibers andbinder polymer, and sretching said composite sheet whereby to form awater vapor-permeable sheet. In general, the extent of stretch in one ortwo directions, and the degree of adhesion between fiber and binderaffects the size of the channels or pores formed adjacent the fibers, i.e., the degree to which th channels approach a wholly annular form.

The expression relatively extensible material, as used herein, meansthat the material must be stretchable under. the stretching forces to beemployed and must elongate during the stretching and substantiallyrecover upon releasing the stretching forces. The expression relativelynon-extensible material means that the material stretches to asubstantially lesser extent, if at all, than the relatively extensiblematerial under the stretching forces imposed.

The steps of swelling and deswelling (shrinking) structural fibers in afiber-reinforced polymeric sheet or film also result in breaking theembedded fibers away from th binder polymer,'i. e., breaking theadhesive bonds between fibers and binder; and this also formsinterconnecting contiguous channels or pores in the sheet. Theswelling-deswelling treatment is disclosed and claimed in copendingapplication Serial No. 325,689, I. .C. Richards','filed December 12,1952, now abandoned. This processcomprises associating liquidswellablestructural fibersand soft, initially thermoplastic polymeric bindermaterial having a softening temperatur below the softening temperatureof said fibers to form an initial sheet,

hot-pressing the initial sheet at a temperature above the softeningtemperature of said binder and below the softening temperature of saidfibers, whereby to form an essentially impermeable composite sheet,soaking said composite sheet at a temperature between the softeningtemperature of said binder and of said fibers in a liquid which swellssaid fibers,'and thereafter drying the sheet at a temperature which isno greater than the softening temperature of the binder. polymer and isusually below the softening temperature of the binder polymer. Thedegree to which the contiguous channels 'or pores therein approach awholly annular form depends mainly upon 2 liquid is a solvent for thepore-forming fibers, the step of swelling the structural fibers andextracting the poreforming'fibers may be carried out in a single step.

, The softening temperature of the thermoplastic binder polymer is thesecond order transition temperature. (Tm) in the case of a normallyamorphous polymer,

or, inthe case of a crystalline polymer, the softeningtemperature is thebeginning of r the melting point range or the temperature at which thecrystalline phase begins to disappear at anappl'eciablerate, asdetermined by X-ray examinationor other. suitable technique. The

' second order, transition temperature of an amorphous polymer isdefined as the temperature at which a dis;

continuity occurs in the curve ofa first derivative thermotcan'beobserved from a ploitof density, linearexpan- 'sion, specific volume,specific heat, sonic modulusor index'of refraction against temperature.United States The liquid I used.

Patent No. 2,556,295 to Pace discloses specific steps involved inmeasuring the second order transition t mperature of an amorphouspolymer. Copending application U. S. Serial No. 325,689, filed December12, 1952 in the name of J. C. Richards, also discloses a procedure ofmeasuring the second order transition temperature of an amorphouspolymer. In the case of a crystalline polymer, the softening pointthereof, as related to the temperature at which the swelling step of thepresent process is carried out, is the temperature at the lower end ofthe melting point range. This temperature is further defined as thelowest temperature at which the crystalline structure beings todisappear at an appreciable rate, as measured by any of the knowntechniques such as X-ray examination, infra-red studies, or by themeasure of heat content as carried out by Raine, Richards, and Ryder andreported in Transactions of the Faraday Society, 41, 61 (1945). In thisstudy, for example, a sample of polyethylene was found to have a meltingpoint range from 90 C. to 104 C.;'i. e., at 90 C., half of thecrystalline structure remained.

Subjecting a fiber-reinforced sheet to a combination ofswelling-deswelling and stretching, such asis disclosed and claimed inthe copending application of Harold L. Mighton, Serial No. 430,550,filed May 18, 1954, is more effective than either stretching alone, orswelling and deswelling alone, for breaking the bond between fibers andbinder polymer, since such a combination process serves to create agreater volume of void space in the treated sheet; i. e., the contiguouschannels or pores formed are more advanced toward a wholly annular formthan contiguous channels or pores formed by either stretching alone orswelling-deswelling alone.

in general, the leather replacement sheets of the present invention areprepared by forming a substantially water vapor-impermeable, compactedsheet of a polymer reinforced with structural fibers and having integralsurface strata containing uniformly dispersed pore-forming fibers, butno structural fibers, and thereafter treating the said Watervapor-impermeable sheet'by stretching the sheet and/ or soaking thesheet in liquid which swells the fibers, and finally extracting thesoluble pore-forming fibers from the surface strata. The expressionsubstantially water vapor-impermeable as applied to the initialcomposite sheet (i. e., before treating) means that the sheet has aleather permeability value (LPV) of less than 1,000 grams/ 100 sq.meters/hour, measured at 23 C. and 90% relative hurn'idity. 'In generalterms which may be applied to any combination of relatively extensibleand relatively none'xtensible materials useful in the present process,the

7 water vapor permeability of the initial composite base sheet issubstantially no greater than that of a homogeneous sheet of therelatively extensible material or the the water vapor permeability ofsuch abase sheet is in-z termediate between the permeabilities ofhomogeneous sheets of the two major components-of the base sheet.Actually, the leather permeability values (LPV) of the initialcompacted, substantially water vapor-impermeable sheets-which aretransformed into permeable sheets by following 'theprescnt processarelow not only because the sheet is'compacted by hot-pressing, but alsobecause, of

the thickness of the sheets'which are useful for converting Q dynamicquantity .of the polymer with temperature. It;

to leather replacement sheets. That is, theinitial sheets are usuallybetween 0.0l5-0.05" in thickness, and homo low LE3! s. Normally, theLPV'is appreciably less than l,000,"an d in no case greater.

;A clearer understanding of. processes of forming the leatherreplacementjcompositions of the present invention and the structure. ofthe compositions themselves may be had by referring to the'accompanyingdrawings wherein:

Figure 1 is a flow diagram of a process of making the present leatherreplacement sheets by stretching a hotpressed sheet comprisingstructural fibers, a binder polymer and strategically positioned, thatis, positioned in a surface stratum, soluble pore-forming fibers, andthereafter extracting the pore-forming fibers;

Figure 2 is a flow diagram of the necessary steps of another embodimentof the process of this invention, namely, one involving simultaneouslyor separately swelling structural fibers and extracting strategicallypositioned, that is, positioned in a surface stratum, poreforming fibersby immersing the initial sheet in a liquid, and thereafter deswellingthe structural fibers by drying the resulting sheet to remove liquidfrom the structural fibers; and a Figure 3 represents a flow diagram ofa series of steps leading to the preparation of the present leatherreplacement composition wherein alternative steps for preparing thesubstantially impermeable, initial compacted sheet are presented, andthe initial sheet is made porous by a combination of stretching andextraction or by a combination of swelling-deswelling and extraction.

In referring to the accompanying flow diagrams, it should be understoodthat the cross-sections of typical lay-ups and sheets (in variousstages) represent a minimum structure. In other words, stage A of Figure1 illustrates compositing three essential types of strata, namely, alayer of pore-forming fibers (layer 6), a layer of binder polymer (layer4), and a layer of structural fibers (layer 2). These layers may varyconsiderably in thickness, this depending on the thickness of theultimate desired leather replacement sheet. On the other hand, as

many additional alternate layers of binder polymer and structural fibersas practicable may be included in the initial lay-up, as will beillustrated in the examples to be presented hereinafter.

The nature of the initial fibrous polymer sheet, that is, the relativepositions and distribution of structural and pore-forming fibers,determines the properties of the final leather replacement compositions.A lay-up or composite of essential components is shown in stage A ofFigure 1. That is, a web of structural fibers 1, for example, nylonfibers, forms the lower layer, layer 2. On top of this mat or sheet ofnon-woven fibers is placed a homogeneous sheet of a binder polyer 3,layer 4, for example, a blend of polyethylene and polyisobutylene (50/50). Finally, layer 6 is placed upon the composite, layer 6 being a webof pore-forming fibers only. The lay-up" may, of course, be comprised ofa plurality of layers of each type so long as the statedrelativedisposition of structural and pore-forming fibers is maintained.

7 face strata containing pore-forming fibers, but no structural fibers.Step 2 involves stretching the sheet of stage B in one or twodirections, the'film being elongated anywhere from to in one or bothdirections, that is,

step is embodied in the process of Simril, described and claimed incopending' application U. S. Serial No. 318,732. in stage C, thefiber-reinforced film is porous as a result of the stretching step. Thatis, the stretching has served to stretch the binder polymer to a greaterextent than the embedded fibers so that the binder polymer has beenbroken away from around the fibers; and interconnecting channels orpores 7 contiguous with the in directions perpendicular to each other.This stretching I6 fibers have been formed in the film or sheet.However, in stage C, the upper surface still contains the poreforming orextractable fibers. Hence, upon abrasion, the surface of thiscomposition would fuzz because the abrading action would raise thefibers to the surface in the form of fuzz. Therefore, step 3 involvesextraction of the pore-forming fibers from the surface of the poroussheet of stage C, whereby to form pores 8 in the surface stratum of thesheet. It is important to emphasize that this extraction process may becarried out relatively rapidly compared with the extraction of solublefibers from within a fiber-reinforced sheet containing soluble fibersthroughout the entire cross-section. This is because the solventpenetrates rapidly into the shallow surface strata containing thesoluble fibers. Furthermore, stretching the sheet prior to extractionfacilitates rapid penetration of solvent into the sheett. Stage D,therefore represents a porous fiber-reinforced polymer film havingintegral porous surface strata having no fibers.

Referring to Figure 2, another process of preparing compositions of thepresent invention is illustrated. Stage A represents a composite oraggregation of essential components, as in Figure 1, wherein layer 2 isa nonwoven fibrous mat of a structural fiber 1, for example, nylonfibers. Layer 4 is a homogeneous film of a binder polymer 3, forexample, polyethylene or a melt blend of polyethylene andpolyisobutylene. Layer 6 is a nonwoven fibrous mat of extractable orpore-forming fibers 5, for example, in this illustration, polyvinylalcohol. The composite of stage A is then hot-pressed in accordance withstep 1 to cause the binder polymer to flow around the lattice ofstructural and pore-forming fibers to impregnate the fibers. Thecompacted sheet of stage B is an impermeable, thatis, substantiallyimpermeable to water vapor and air, polymeric film or sheet reinforcedwith structural fibers and having the upper surface stratum containingextractable pore-forming fibers. Step 2 involves immersing a compactedsheet of stage B into a hot liquid medium at a temperature above thesoftening temperaturee of the binder polymer, for example, hot waterwhen polyvinyl alcohol is the composition of the pore-forming fibers,which medium serves to swell the structural fibers and extract thepore-forming fibers from the upper surface stratum of the sheet. Stage Cillustrates the condition of the soaked sheet immediately after removingthe sheet from a hot liquid medium. In stage C, the upper surfacestratum is porous (pores 8), i. e., is devoid of pore-forming fibers;and the structural fibers inthe lower portion of the sheet are swollenby the absorbed water. Furthermore, the polymer binder is considerablysoftened as a result of being soaked in a liquid medium at a temperatureabove the softening tem perature of the binder. Step 3 involves dryingor removing the liquid medium from the structural fiber at a temperaturebelow the softening temperature of the binder polymer. The resultingproduct of stage D is porous throughout as a result of a deswelling ofthe swollen structural fibers; that is, the structural fibers shrink totheir normal dimensions when the sheet is cooled and dried at atemperature below the softening temperature of the binder polymer.Shrinkage (des'welling) of the structural fibers away from the adjacenthardened polymeric binder polymer (the softened, i. e., softened duringsoaking in a hot liquid, binder polymer is deformed when the structuralfibers are swollen) results in forming channels or pores 7 contiguouswith the structural fibers, thereby forming a porous structure. Hence,stage D illustrates a porous fiber-reinforced polymer film or sheet rousfiber-reinforced sheet having integral a porous sur- "7 face stratumsubstantially free of fibers. Figure 3 illustrates the series of stepsrequired to form, by a somewhat dilferent procedure than thatillustrated in Figures 1 and 2, a leather replacement composition of thepresent invention by a combination of extraction and stretching orextraction of pore-forming fibers and swelling-deswelling of thestructural fibers, for example, structural fibers of nylon. Thesuperimposed mats 9 and 10 of structural fibers 11, shown in stage A,are impregnated (step 1) by conducting the mats through a solutioncontaining a suitable polymer 12; the polymer may be dissolved in asolvent; orthe polymer may be dispersed in a non-solvent medium. Stage Billustrates the superimposed webs after having been impregnated with apolymer. volves hot-pressing the impregnated mats to compact the sheet.Since pore-forming fibers are to be pressed into the upper surfacestratum of -the sheet, this initial compacting step should not becarried out at a temperature high enough to cure the binder, thatis,when a curable binder is used. Stage C'represents the compactedfiberreinforced impermeable sheet. Step 3 involves coating the compactedsheet with, for example, a dispersion of pore-forming fibers 13 in anon-solvent medium, which may or may not contain a dissolved polymer.This leads to stage D, which shows the compacted fiber-reinforcedpolymeric sheet having pore-forming fibers deposited as a surfacestratum 14. This composition is then subjected to step 4 which involveshot-pressing the pore-forming fibers into the surface stratum of thesheet, and completing the compacting of the sheet. The resulting productis illustrated as stage E. In accordance with the procedures describedin Figures 1 and 2, the product in stage E may be subjected to astretching step, that is, stretching in one or both directions to form aproduct in stage F. The product of stage F is permeable to water vaporand air, but still contains pore-forming fibers inthe surface stratum.-Consequently, the product of stage F is subjected to an extraction stepwhich removes the soluble fibers from the surface stratum. Hence, stageG represents a fiber-reinforced porous sheet or film having a poroussurface stratum free of fibers. On the other hand, the sheet of stage Emay be subjected to a simultaneous extraction and swelling step byimmersing (step A) the sheet in a liquid (at a temperature above thesoftening temperature of the binder polymer) which dissolves. thepore-forming fibers and swells the structural fibers. As the net resultof such a step, stage F represents a sheet having the pore-forming orsoluble fibers removed from the surface stratum and having thestructural fibers in swollen form. This product is then cooled andsubjected to a drying step at a temperature belowthe softeningtemperature of the polymeric binder to remove the swelling liquid fromthe structural fibers to permit them to return to their originaldimensions. Hence, stage G represents a porous fiber-reinforced film orsheet having a porous surface stratum containing no fibers.

As an alternative procedure of depositing pore-forming fibers upon thesurface of compacted fiber/ binder sheet, i. e., step 3 of Figure}, thefibers may be deposited from a solution containing a dissolvedpolymerwherein the pore-forming fibers are present as a dispersed phase.For example, polyethylene may be dissolved in hot toluone, and polyvinylalcohol pore-forming fibers maybe present as a dispersed phase. Uponcoating the surface of a compacted fiber/binder sheet with thiscomposition and evaporating the solvent, the coating takes the form ofafilm of polyethylene having fibers of polyvinyl alcohol dispersedtherein. The coated fiber/binder sheet is then consolidated byhot-pressing the sheet, and the coating becomes integral with the sheetproviding there is sufficient adhesion between the polymer of thecoating and the binder polymer of the initial fiber/binder base sheet.This procedure serves a dual purpose in that it provides a method ofstrategically distributing pore:

forming fibers in the surface stratum of a sheet, and it Step 2inprovides a method of preparing a porous fiber/binder compositionhaving a surface which is harder, tougher and more resistant todestruction by scufiing or abrasion than the binder polymer in theinternal structure of the sheet. On the other hand, the binder in theinternal structure is much more pliable and flexible than the binder inthe surface stratum, the overall structure being highly flexible buthaving desirable surface properties. It should be emphasized that thebinder employed in the surface stratum must adhere strongly to theinternal binder. For example, polyisobutylene may be employed as theinternal binder, and polyethylene may be employed in the surfacestratum; and since polyisobutylene and polyethylene adhere stronglyunder heat and pressure, an integral structure is formed after thecoated sheet is consolidated.

Although it is most expedient in treating the initial compacted(substantially impermeable) sheet to extract soluble pore-forming fibersand swell the structural fibers simultaneously, i. e., the sheet isimmersed in a liquid which simultaneously extracts pore-forming fibersand swells structural fibers, the sheet may be immersed first in anon-solvent medium to swell structural fibers, dried to deswell (shrink)the fibers, and finally immersed in a solvent to extract pore-formingfibers. On the other hand, the pore-forming fibers may be extractedprior to stretching the sheet, but preferably the stretching step iscarried out first because it opens pores in the sheet, and thisobviously facilitates penetration of solvent for extracting pore-formingfibers from the surface stratum.

Furthermore, it should be pointed out that it may be advantageous undercertain circumstances to stretch the compacted sheet first to only aslight degree, i. e., 10-20% in one or two directions, in order to openthe structure of the sheet and facilitate penetration of the solventinto the surface stratum. This step may then be followed by extractionof pore-forming fibers from the surface stratum, and thereaftercompletion of the stretching step by stretching the extracted sheet anadditional 30-40% in one or two directions.

As described hereinbefore with reference to the accompanying diagrams inthe form of fiow charts, the particular process steps which may beemployed to produce a particular substantially non-fuzzing leatherreplacement composition of the present invention may be varied. in allcases, however, it is essential that a pore-forming fiber beincorporated into the surface stratum of the initial composite sheetbefore the sheet is subjected to any of the basic processes orcombinations thereof de- 7 fiber of the fibrous components. This isaccomplished by forming a lay-up or composite of the essentialcomponents. of the fiber-reinforced sheet, it being essential that thesecomponents be composited in a strategic order for the purpose of placingthe particular type of fibers, that is, the structural and pore-formingfibers, in particular positions throughout the crosssection of the sheetfor the purpose of producing a porous fiber-reinforced compositionhavinginterconnecting pores contiguous with the fibers which aredistributed substantially uniformly throughout the sheet below thefiber-free surface stratum. It is obvious that in every case a layer ofporeforming fibers must be strategically positioned in the initialcomposite, that is, before final compacting, so that the compacted sheetcontains pore-forming fibers distributed uniformly in the surfacestratum thereof. 0 viously, it is entirely within the scope of thepresent invention to incorporate pore-forming fibers in 'both the u perand lower surface strata of a compacted sheet so that the ultimate watervapor-permeable composition amuse has both surfaces which are porous butfree of structural fibers. It is also essential in preparing the leatherre-- placement compositions of the present invention to position thestructural fibers in the initial composite sheet so that, aftercompacting, the structural fibers are uniformly distributed throughoutthe cross-section of the compacted sheet, but are absent from thesurface strata which contain solely the pore-forming fibers. Techniquesof accomplishing the strategic positioning of various types of fibersalong with suggested processes of impregnating these fibers with apolymeric binder have been illustrated hereinbefore with reference tothe accompanying diagrams.

As mentioned above, the initial composite (uncompacted) sheet issubjected to a hot-pressing or consolidiating operation which causes thebinder polymer to melt and flow, this resulting in thoroughlyimpregnating the meric binder to form a continuous solid polymeric filmor sheet. The hot-pressing step must be carried out at a temperatureabove theflow temperature of the polymeric binder (flow temperature, forexample, may be determined by ASTM test D'69-48) and below thedeformation orsoftening temperature of the fibrous coniponents.Generally, the compositions are hot-pressed at a temperature within therange from l20-200 C. under pressures varying from 50 pounds per squareinch to 2,000 pounds per square inch. In all cases, the temperature atwhich the fiber/binder sheet is consolidated must be below thedegradation temperatures of the fibrous components and the binderpolymer. During'the hot-pressing step, the fibrous components, whichmust not be deformed to such an extent as to lose their identity asfibers, or be transposed to the extent that a considerable portion offibers aremore concentrated in one'por- I tion of the sheet than inothers, serve as a lattice around which the polymeric binder flows toimpregnate each and every fiber. Hence, after consolidation, the sheettakes the form of a fibrous lattice which is completely embedded orsurrounded by the binder polymer.

In this form, the compacted fiber-reinforced polymeric film or otherhand, the process of stretching a fiber-reinforced sheet, which is morefully described in the above mentioned copending application U -S.SerialNo. 318,732," produces a fiber-reinforced sheet having channels orcapillaries contiguous with each structural fiber which has been brokenaway (the adhesive bond between the structural fiber and the binderpolymer has been broken) from the binderpolymer. The .technique ofswellingdeswellingyof thei'structural fibers" also serves to breal;

the adhesive bond between the'structural fibers and binder polymer; and,consequently, the channels or cap-' -illaries formed are also contiguouswith the' structurah .fib'ers. it is also'tliebinderj'polyme'rwhichholds together and is'rein'forced by the"'structtiralifibere j "Generally,

the binder polymer may beselected from a great variety which includepolymersg'ener'ally classifid as elastoniers.

The polymeric'binder, in general, shou'l'db' .toughQpIiJ able, andelastic; and it should be atleastinitia'lly thermoplastic and shouldmelt and flow at a ternperature. be-

low the deformation, (softening) "1 Pratures of the structuralfiber andpore-forming fiber. By the tenn- -initially thermoplasticiis meant thatthe binder'rnaterial; must melt and-flow ,u nd er the] conditions of thehot-L 1. Tensile strength should be at least 500 p. s. i.

2. The elongation must be at least v 3. Materials not having a tensilestrength and elongation greater than the above minimum specificationsmay be satisfactory if the product of their tensile strength andelongation (where 100% equals 1) is at least 1,000.

4., The tensile modulus must not bemore than 25,000

p. s. i. and, preferably, not more than 5,000 p. s.

A number of specific thermoplastic binder polymers useful for purposesof this invention and classified as elastomers are disclosed by H. L.Fisher (Industrial and Engineering Chemistry, August 1939, page 942).The binder polymer employed should be chemically dissimilar to thestructural and pore-forming fibers.' Because. of their readieravailability, better properties, and

appreciably better ease of handling, the addition polymers arepreferred. A particularly outstanding group are the additionpolymerscontaining in combined form the ethylenically unsaturated monomersincluding both the mono and diene-type monomers. The most outstandinggroup of these addition polymeric binders are the vinylidene polymersand copolymers including both the monoene and diene types. ischaracterized by having ineach polymerizable monomer therein involved asthe only polymerizable ethylenic unsaturation, terminal ethylenic groupswherein the terminal carbon is a methylene carbon, i. e., thosecontaining one or more vinylidene (CH2=C=) groups. 'Included in thismost preferred class are the great majority of commercially availableaddition polymers. Specific examples of such polymers include thevarious vinylidene hydrocarbon'polymers such as butadiene/styrene,polyethylene, polyisobutylene, polyisoprene, both synthetic andnatural;- the various negatively substituted polymers and polyvinylfluoride; derivatives of such polymers as halogenatedvinyl andvinylidene polymers, e. g., chlorinated polyethylene, and chlorinatedpolyvinyl chloride the various vinylidene polymers wherein one or bothof the indicated free valences of the 2-carbon of the vinylidene groupare bonded directly to carboxyl groups or' groups hydrolyzable tocarboxyl groups either directly to the acyl carbon or the oxy oxygenthereof, such as poly mers of various vinylidene, esters, includingvinyl acetate and ethylidene diacetate; vinylidene carboxylic acids andtheir derivatives such as, acrylic acid, acrylonitrile, andmethacrylamide. Also included in this most preferred groupare thevarious copolymers of such vinylidene monomers',' includingspecificallythe various inonoene 'lofsoft', elastic, initiallythermoplastic, synthetic polymers and diene 'copolymers of this classsuch as 2,3-dichloro- I P :butadiene-l,3/2-chlorobutadienr1,3copolyrners; the varj i ous.mundane/vinylidene copolymers-suchas thecom. mer,cially.important vinyl ,and vinylidene chloride co-- 1polymers, ,e. g, yinyl chloride/ vinyl acetate, vinyl ch10.ride/vinylidene chloride, andfvinyl chloride/vinyl acet y n tril j.roppy the r us vi ny i ne r s djrocarbon'negatively substituted vinylidenecopolymers, e. g. ethylene/vinyl.acetateand thehydrolyzed productstherefrom; ethylene/vinyl chloride, and butadiene/acry' lonitrilecopolymers. 3

"In the case of those binder: components t :ontaining in combined formappreciable proportions of diene mono! mers, particularly the.vinylidene diene monomers, it is This class of polymers frequentlydesirable to have present in the solution, dispersion, or bulk treatingmaterial, whichever is used, suitable amounts of chemical agents foreffecting under controlled conditions, after the fiber has beenimpregnated with the binder and the whole mat suitably compacted, thecross-linking of the diene copolymer component. These chemical systemsfor effecting such controllable cross-linking are well known in therubber art and, in the case of the diene hydrocarbon polymers andcopolymers, such as 2-chlorobutadiene-l,3(chloroprene), normally.function through a disulfide formed cross-link arising from the presenceof mercaptans and/or sulfur in the diene polymer composition; and in thecase of such polymers as chlorosulfonated polyethylene, curing may becarried out in the presence of metallic oxides such as zinc or magnesiumoxides.

Various polyesters containing terephthalic acid or derivatives thereof.as essential components are also useful as binder polymers, theseincluding polyethylene terephthalate and copolyesters made from ethyleneglycol, terephthalic acid'and sehacic acid of the general type describedand claimed in United States Patents Nos. 2,623,031 and 2,623,033 in thename of M. D. Snyder. Polyamides useful as a binderpolymer includeN-methoxymethyl polyhexamethylene adipamide and other similar polymersdisclosed and claimed in United States 7 Patent No. 2,430,860. Alsoincluded among useful binder polymers are the polyvinyl acetalsfsuch aspolyvinyl butyral, polyvinyl laural, etc. Included among variouselastomeric polymers which may be employed as binders in the presentinvention are the polyurethanes which are essentially reaction productsof (1) an organic polyisocyanate or polyisothiocyanate with (2) acompound "obtainable by reacting (a) one or more polyhydric alcoholswith (b) one or more polycarboxylic acids (either in the presence orabsence of one or more monocarboxylic acids). Specific products of thistype are described and claimed in United States Patent No.

deficient in drape, hand, and flex life, and, more importantly, isusually particularly deficient in tear strength. A convenient rule forcharacterizing the chemically dissimilar polymeric binders is that theybe incompatible in the melt with the polymer-from which the structuralfibers are formed. a

In many instances, it is desirableto have present in the bindercomposition appreciable proportions of plasticizers, now well known inthe art, for the binder polymers.-

This is particularly important in the case of the vinylidene resins, toprevent formation of products of too great stiffness, espectially' withthe higher molecular Weight, negatively substituted vinyli tlenepolymers and copolymers,. such as the vinyl chloride/vinylidene chlorideand vinyl.

chloride/vinyl acetate copolymers, so as to produce leather-likeproducts of good drape and high pliability.

Suitable examples of these include the higher molecular weight monoordicarboxylic acid/ alcohol or polyolesters such as glycerol mono-oleate,glycerol sebacate, dioctyl' phthalate, and ethylene 'octanoate; 'orthelower molecular. weight polyesters and polyethers such as thepolyalkylene oxides and their esters, e. g., polyethylene oxide,methoxypolyethylene glycol;and the. lower molecular weight condensationpolyesters such as polyethylene glycol adipate.

The binder material may be incorporated into the initial impermeablecompositesheet in a variety of ways, several of which have beenillustrated hereinbefore. The binder material may be in the form offibers which may be carded along with the structural fibers and thepore-forming fibers to form a composite sheet by pressing the cardedmixed fibers at elevated temperatures. Webs or mats of mixtures ofstructural fibers, pore-forming fibers and binder polymers may be formedby mutual, coagulation of a mixed dispersion of the three components. Afibrous mat of a mixture of structural and pore-forming fibers may beimpregnated by dipping or spraying with a binder polymer which may bedispersed in a nonsolvent, e. g., aqueous medium, or may be in a solventsolution. On the other hand, a fibrous mat containing both structuraland pore-forming fibers or just structural fibers may be impregnatedwith a binder polymer in the form of a hot melt. A fibrous mat ofstructural and pore-forming fibers or structural fibers alone may beimpregnated with a binder polymer by calendering techniques or byspraying the binder material from an aqueous dispersion or solventsolution ontoone or both sides of the fibrous mat, followed by theapplication of heat and pressure to impregnate the fibrous portion ofthe mat with the binder material. Regardless of the technique employedto form a composite sheet, the sheet is compacted prior to extraction ofthe soluble or pore-forming fibers by pressing at a temperature abovethe flow temperature of the binder and below the softening ordeformation temperature of the structural fiber and pore-forming fiber.

The binder polymer in the surface stratum of the leather replacementcompositions of this invention may be different from the binder polymerof the internal or base strata. The purpose of this is to obtain a sheethaving maximum flexibility and maximum surface hardness and resistanceto destruction upon scuffing or abrasion. The binder polymers mustadhere strongly to each other in order to form an integral sheet uponconsolidation of the sheet under heat and pressure. Still another meansof obtaining a highly flexible leather replacement having a surfacewhich is hard, tough and resistant to destruction on abrasion is toemploy the same binder polymer throughout the composition, but employhomogeneous sheets or films of the binder polymer (in the initiallay-up) containing varying amounts of a plasticizer. For example, thesheets or films of binder polymer in the internal structure may containas much as %plasticizer while the uppermost sheet of binder may beunplasticized.

Any fiber having substantial strength and which is substantiallyinsoluble in the solvent employed to extract the pore-forming fibers ofthe surface stratum of the sheet maybe employed as the structural fiber.Fibers of nylon, i. e., synthetic linear polyamides such aspolyhexamethylene adipamide, polyhexamethylene sebacamide,polycaproamide and interpolyamides, etc., are outstanding for use as thestructural fibers in the leather replacement compositions of the presentinvention. The use of nylon structural fibers produces a porouscomposition having high tear strength, tensile strength, softness andflex life. In general, however, resultant's'uperior physical I;properties are obtained when the structural fibers are orientedsynthetic linear condensation polymers, e; g., the polyamides, thepolyesters,polyesteramides, mixtures or blends thereof, suchas thedibasic acid/diamine or amino acid polyam'ides', the dibasic 'acid/diolor hydroxy acid/ polyesters, 'or theintermixed polyester/polyamideproducts by now well known in the art and described in greater detail inUnited States Patents Nos. 2,071,250, -25l, -253,

of the structural fibers may be varied according to the '1 generalstrength of properties required. Structural fibers as short as 0.01" maybe employed, but structural fibers having a length of about 1.5"give aproduct of substantially optimum strength properties. Using structuralfibers longcr than 1.5" imparts little additional strength 7 to thepresent leather replacement compositions; but, as

2,130,948, 2,z24,037-'2,572,s44, and the like. The length 7 -13mentioned hereinbefore, it may be convenient to use longer fi rs; andthe use f l ng tructural fibers,"e. g 1 1 to. 8", is thin the intendedscope of the present invention. On the other hand, structural fibersless than 0.01 in length add little to the strength of the sheet overthat of a sheet composed wholly of the binder polymer.

Other types of structural fibers which may be used, particularly in theform of mixtures with poly-amide, polyester, or polyesteramide typefibers, include fibers of cot ton viscose and acetate rayon, wool,polyacrylonitrile, acryloni-trile copolymers, polyvinyl acetals, andglass. It should be emphasized that a considerable advantage may begained by employing mixtures of difierent types of structural fibers,the particular mixture depending upon the particular combination ofprocess steps to be used in making the initial compacted sheet porous.For example, a combination of sWelling-d-eswelling and extraction is tobe carried out, there is an advantage in employing a quantity ofstructural fibers which are more readily swollen by water than nylonfibers, for example, viscose fibers. Hence, a mixture of viscose rayonand nylon fibers may be advantageous, or, mixtures of viscose rayon andpolyethylene terephthalate fibers, or mixtures of all three.

Cellulose acetate fibers are readily extractable using acetone, and somegrades of polyvinyl alcohol are readily extractable with waterp Other.suitable pore-forming fibers are those ofsodium :alginate, potassiummetaphos-j phate polymer glass, and carboxymethyl cellulose. A

Products of satisfactory leather permeability may be formed usingpore-forming fibers as short as 0.01", e.' g. 0.01" celluloseacetate'fiock. However, a considerable increase in leather permeabilityis realized when longer pore-forming fibers are employed. For example,increasthe length of the pore-forming fiber from, 0.01" up to a lengthof 0.25" produces a substantial increase in the leather permeabilityofthe resulting product. How; ever,- an increase in pore-forming fiberlength from 0.25"

to 0.5 generally results in substantially no increase in the leatherpermeability of the resulting sheet.

Variations in the denier of the structural fibers and pore-formingfibers appear to have-little efiect upon,

leather permeability. "On-the other hand, it has been 14 ot the Pre-forming fiber in the solvent, the temp ra u of the extracting liquid,and the degree of agitation, and the ease with which the solvent canpenetrate the sheet. It is within the scope 'of the present invention toemploy a liquid (as a solvent) which degrades the poreforming fibers,while not afieoting the structural fibers or binder polymer, but whichliquid dissolves the degradation product, that is, dissolves thedegraded pore-forming fibers and thereby extracts them from thefiber/binder sheet. On the :other hand, the fibers may be degraded withan acidic or basic liquid follow-ed by the step of dissolving out thedegraded fibers wit-hanother liquid such as water. 7 a

On the basisi'oiFnumerous types. of wearing comfort tests, it has beenascertained that membranes, e. g., leather and leather replacements,exhibiting a leather :permeability of 2,000 to 10,000 grams/100 sq.meters/hour would provide'wearing comfortequivalent to that obtained*with'glazed leathers and heavy shoe upper lea-thers. Furthermore,permeabili-ties -of-10,000 to 22,000 were found to provide adequatewearing comfort equivalent to that obtained with the lightest shoeleathers.

In preparing the leather'replacement compositions of this invention inaccordance with a stretching extraction technique or by the process ofswellingdeswelling and extraction, the weight ratio of binder polymer tostructural fiber in the initial substantially impermeable compactedsheet may vary from 30:70 to 70:30. However, the optimum quantity ofbinder material in the initial composite sheet ranges from 40 to 60%based upon the total weight of the two major components, that is, thebinder and the structural fibers. In each case, the poreforming fibersare uniformly distributed only within the surface stratum; and theweight of these soluble poreforming fibers normally ranges between 5%"and 25 based upon the total weightof the fibrous components in thesheet. Normally, the densities of the binder polymer and the structuraland pore-forming fibers are relatively close; and in such cases, theratio of the components may be expressed on either a volume or weightbasis. Generally, as the quantity of binder polymer in the compositionis reduced, the initial composite compacted sheet becomes more and morepermeable to water vapor (the stretched sheet or a sheet subjected tosWelling-deswelling' is highly permeable by comparison); but otherproperties (particularly strength) and characteristics of the finalsheet, i. e., the stretchedsheet or one subjected to swelling?deswelli'ng, are not satisfactory for use as a ieather re- 1 tity ofbinder material feel more like felt instead of found that decreasing thethickness of the pore-forming tfiber results in forming a leatherreplacementflsheet having improvedgreslstance to penetrationby liquidwater,

In general, it may be said that fibers which are finer than one denierare dilficult to process. on standard textile machinery. Furthermore;the greater the fiber denier, the greater is the tendency of the fiberstoshift within the binder*u'ndertearingand flexing this action ingeneral making the product more durable. At the other extreme,

fibers coaser than 16 denier areextr'emely harsh and 7 more closelyresemblebristles. v I

The solvent shoul "dyed or :p're pigmented structural fibers. :color'edsheetmaterial is prepared by the "use of dyed or leather, and thetensile strength .and tear strength are appreciably below the tensileand tear strength of similar compositions having from 40-'60% ofthebinder polymer present. 'This is because in most cases the amount ofbinder polymer is insufficient to hold the structuralfibers On the otherhand, as the amount of binder. polymer is increased, the initialcomposite sheet has properties approaching those of a homogeneous filmor7 together.

sheet of the binder polymer.

' ,Color may be imparted to the sheet material of this invention byincorporating dyes or pigments in the polymericbinder, or by dyeingafter finishing or using pre- Preferably,

' pigmented structural fibers or by incorporating the coloringmat in thepolymeric binder, since the sheet material I is then' uniformly coloredthroughout; andfthus, unlike colored natural leather, itwillqnot exhibitanymar'kedor-v r undesirable color change ifscutIe-d or abraded. Whenpigments are incorporated into the polymer binder'ior "the purpose ofpreparing colored sheets, the concentration of pigments shouldbe kept ata minimum, less than 510%, by weight of the total sheet, tin-order thatthe physical properties ofthe sheet, particularly tensile 15 strength,tear strength and abrasion resistance are not materially affected.

In following the process of the present invention, the creation ofinterconnecting pores or voids in the final 1 6 ment comprising twowheels. One wheel was nonrotatable and was 6. inches in diameter and 1inch in width. On the periphery of this wheel was mounted a sample ofthe sheet to be tested. The second wheel was foregoing example, wasdetermined in a simple test instru sheet may be enhanced by distributingpore-forming fibers made of felt, and it was 4 inches in diameter and 1inch throughout the entire cross-section of the sheet. C-onsen Width-The f l Wh l ta d about an ff-C r aXiS quently, interconnecting voidsare then formed by ex- (resulting in an eccentric motion), and the axiswas so tnaction-of pore-forming fibers and by stretching the sheet posioned th h axim m displace ent of he f l and/or by swelling-deswellingthe sheet, this being highly Wh el it abraded strongly against the sheetsample useful when it is desired to form a leather replacement 10mounted n th l rg r non-mtata l Whe l- A single TO- by combining aparticular binder polymer with a particutation of the offcenter wheelwas referred to as a scuff. l-ar fiber which adhere to each other to adegree greater than that normally practical when stretching and/or'EXAMPLES INCLUSIVE- ge i8 h as the mY means impart In the followingexamples, 2-5 inclusive, the binder mg. porosity to a particularfiber/binder sheet. On the polymer was incorporated into the initialcomposite i other hand, It must be p t t h greatest e the form of films(0.002" in thickness) of polyethylene. vantage ofihePmscut Process iswith F? foft-11mg The structural fibers were carded webs (weighing aboutporous fiberreinforced polymer sheets exhibiting an out- 11 grams/Sq ft) f nomwoven polyhexamethylene standing resistance to surface fuzzingupon scuffing by adipamide fib 1 in length and 3 denier 51 virtue oftheir having substantially no structural fibers m The pore forming orSoluble fibers were in the or particles-1n the surface stratum. form ofmats (weighing about 5.5 grams/sq. foot) of non- The followmg examplesW111 serve further lnustrate woven cellulose acetate fibers (2" inlength and 3 denier the nature of and techniques of preparing theleatherreper filament) The initial 1 was composed f alter. P1acment ,composmonsof h P mventlon- Parts nate layers of webs of structural fibers andfilms of polywelght unless Otherwlse mdlcafted' ethylene, the bottomlayer being a web of fibers and the uppermost binder layer being ahomogeneous film of EXAMPLE 1 polyethylene. The web of cellulose acetatefibers was then A lay-up or composite was formed from three mats placedupon the uppermost layer of polyethylene. There- 13 yard) f nomwovenfibe f poqyhexa after, the composite was sub eeted to heat and pressurein methylene adipamide, 2 5 inches in length and 3 denier accordancewith the conditions recorded in Table I below. per filament, and threehomogeneous sheets or films The mpact d Composite sheet, which wassubstantially thickness) of a 50:50 blend Ofpo1y impermeable, c.,non-porous, was then subjected to ethylene polyisobutylene binder,alternately either a stretching step, that is, a stretch in twodirections posed with a fiber mat lowermost, and a top layer con lf 9 9the compacted Sheet was Immersed sisting of a mat of non-woven'celluloseacetate fibers mto a hqhld which y eq the Structural a P 2 inches inlength and 3 denier per filament. This corn forming fibers. the hquld mat a temperature above posite was subjected to a hot-pressing ,(step 1"of Figthe softening temperature of the binder p ure 1) at a temperatureof 140 c. at 500 p. s; i. for liquid p y for swelling the structuralfibers m three minutesf The resulting compacted, substantially 40 alsoact e a Solvent for the P fi e h impermeable sheet took the form ofstage B of Figure 1. pore'formmg fibers may he extracted from the 5 1Step 2 involved stretching the sheet of stage B in one tion as aSeparate P-) After Swelling t Stflletllral direction to an extentsubstantially equal to 40% elongafibers at a temperature above theSoftening temperature tion., The resulting sheet was then in the formof, stage of the binder P y the sheet Was dried at a C; that is, it wasa porous fiber-reinforced sheet having Pefethfe approximately equal tothe Softening e p soluble pore-forming fibers in the surface stratum. Fitlll'e 0f the m P y m a lower temperaturenally, step 3 was effected; andthis involved soaking the Table I indicates the thickness of the PQI DSsheet, sheet in cold (room temperature) acetone to extract the the unitWeight of the sheet in grams P square r. soluble cellulose acetatefibers. The acetone exerted no. the-leather Permeability Value the e psolvent effect upon the nylon structural fibers'and poly-I P e nd timeof pressing the initial'composite, the ethylene-polyisobutylene binder.The leather permeextent to which the compacted sheet was stretched inboth ability of the resulting sheet, stage D (0.020" inTthi-ckdirections(Whe the Sheet wes'lstfetehed), ahd'the time ness), was within the rangefrom 2,500-4,500 .grams/ 100 and medium in which the compacted sheet wasimmersed sq. meters/hour. Furthermore, the composition was sub to swellthe fibers. All of the sheets subsequent to stretchjected to 20,000scuifs before any fuzz iappearedat the ing or swelling-deswelling wereextracted in acetone for surface. This is in contrast with 50 scutfs,which pr'oten minutes to extract the pore-forming fibers.

Table l Thickness Unit r of Final Weight of LPV (guts/100 PressedStretched, Example Sheet' Final Sheet sq.n1ete1's/ O.,p'.s.i.. percentswelled '(inches), (gins/sq. hour) min. 7

' meters) 0.05380 902 2, 19, 1, 867 140l600/6 30x40 0. 04113 790 3, 681,3, 245 140/350/6- 15 minutesinHzO. 2,632,2,392 140/350/0 ISminuteSinH-O.

-.2,355,2,276 140/350/e zzminutesinH o.

. V EXAMPLES 6-9 INCLUSIVE duced fuzz at the surface of asimila'rcomposition which In the following examples, 6-9 inclusive, the binderwas prepared by stretching a structural fiber-reinforced polymer was inthe form' of films (0.003-0004" in thickpolymeric sheet of the samecomposition, this sheet havness) of a blend of polyethylene andpolyisobutylene ing structural fibers throughout its entirecross-section. (50:50) of polyethylene alone. The structural fibers wereThe-scuff or abrasion resistance, i. e., resistance to surinthe form ofcarded webs (each weighing about 11 face fuzzing upon repeatedabrasions, referred to in the grams/sq. foot) of polyhexamethyleneadipamide (2%" in length and 3 denier per filament). The pore-forming 17fibers were either cellulose acetate or polyvinyl alcohol (in the formof non-woven mats weighing about 5.5 grams/ sq. foot), the particularpore-formingfiber used being indicated in Table II below.

@1 p I EXAMPLE 10 p In this example, the porous sheet was composed .ofthetsamebinder polymer, structural fibers, and pore-forming fibers asthose productso'f Examples 6-8, inclusive.

binder polymer was a mm bylrcast' 5 Furthermore the porous sheet wasformed by stretching in t e film from ahot solution oft e o mers in touene. r A solution of polyisobutylen in tvolupehg was efiected at thelnitlal compacted sheet 30% in both directions; and room temperaturethesolution was heated and polyg pore-formal}? i (cellulose ig? 5 extractedyimmersing' ers eet in acetone. a e II ists anumrefinements; Erratafishers: m of as the film began to solidify, upon evaporation of thesolf gi a range of the same properties of genuine vent, fibers ofpolyhexamethylene adipamide in the form EXAMPLE 11 ofamat were lightlypressed into the surface. Thelay-up g V .7 H r for Example 6 consistedof four layers of the binder j mp ebgnd P y e W38 111 h O Q polymerfilm, upon which were placed two layers (mats) e film e o a q qnbtjr rehlol'lde -d of the structural fibers, four more layers of the binderoctylphthalate (about Q h y y h polymer film, and, finally, a mat ofpore-forming fibers, The uc fibers e e P'P1Y Y e adip'amide in the ordernamed. The lay-ups for Examples 7 and 8 111 g h h vj dc'm and the Pconsisted of four mats of structural fibers alternated with ns fibers eShFfaee strata the compacted four sheets of binder polymer film and atop mat of the ee e P1Y YL e9h9 fibers 111 length and 3 pore-formingfiber. The lay-up for Example 9 consisted l f h eh l I w y- P ofcomponents Was of two layers (mats) of the structural fibers on which em e h a t b ta A of fi e d were placed four films of the binder polymer,two more h e m e 9? rq y m hr adlpamlde Were mats of structural fibers,four more films of the binder SI Y p 1 t e tfi P to eolhplete PQ-polymer, and a mat of the pore-forming fibers, in the l e 9 Solvent h af P Y Y e h order named. The web of pore-forming fibers was ,placedfibers was Pl 9 2, pp m Y of d upon the uppermost layer of binder, andthe composite ly h, T e eqmre g es PK S 170 Under was hot-pressed toforma consolidated structure. .All of 3 P e 9 5- b -[Sqh e f 10 mmutesand there the composites were pressed at 140 C. and 50.0 lbs/sq. fle Fole elQW 9 uhdelf Pr Table III inch for3 minutes. Table Hindicates thethickness of the mdleates h erte tfq Yh Q iht? compacted sheet was.porous sheet, the unit weight in grams per square meter, Stretched bothdll'eetlehs by 30%), and the the leather permeability, the extent towhich the compore'formmg fibers (polyvfnylaleohol) were extracted pactedsheet was stretched in both directions or'the time fi m efill e e PIQ PlQ the Stretched Sheet during which the sheet was immersed in hot water(maini Thef yt p p p li of h fi l dned tained at a temperature above thesoftening temperature he 3 1? 1 1 T b e H and these Properties "f e ofthe binder polymer). In Example 9, the blend of m r d W Ih ?n of thesame Propertles of gemlme polyethylene and polyisobutylene was employedas the leather composltlonsbinder polymer throughout the structureexcept at the T bl 111 uppermost surface of the sheet. For example,films of H the upper four layers of binder polymer were polyethylene 40Physical Property Leather Example Example instead of a film of ablend ofpolyethylene and polyiso- Range 10 11 butylene. This provided for aflexible internal structure y i which, in turn, produced a final sheethaving good fiexihi fi f he (I063 0-0 bility, in addition to a surfacelayer having superior gfii f i fifgtfifff fil lg bfiiig gfifi 38%hardness and resistance to destruction on abrasion. gm hq to hr 3 4 3%Hence, by employing a surface film of the binder polymer LPY JgI%%IQQShTIE6QTE2BE 220-131000 31419; 41937 which is different from the binderpolymer employed ggg fgg ggg 10,000, gg gg i gg gg n na y an integralStructure y be formed, that BinderfPercentj::::: .r -::IIIIII: 42 as aresult of hot-pressing the initial composite; but the 50 Y surface or"the final sheet may be improved by employing a a binder polymer havinggreater toughness, hardness and p resistance to abrasion than the binderpolymer employed A aqueou dispersion of neoprene was prepared, andinterllallY- It Should be emPhaSIZed, W T, that the the compositioncontained the following components: binder employed in areas other thanthe surface of the F f r 1 1 sheet should be flexible and tough; As ageneral pref Fem??? x 1 requisite in selecting a binder for use at thesurface of a 359. 3 qg vu camzmg lsperslon' sheet, the binder polymeremployed at the surfaceshould 1 Parts :5 an exhibit good adhesion to thebinder polymer employed Par s o a ag internally in the Sheet 200 partsof a black pigment.

Table 11 Unit Stretch/Swell. Thickness Weight of 1. Example of The TheFinal LPV PoieFormlng Fiber Extraction Binder Final Sheet Sheet (Per(Min- (inches) (g ns/sq. cent) utes) meters) 6 0.04012 803 2, 745,2,25230x30 Celluose lam Acetone,10minutes- Polyethylene/Polyhebutylene,50/50. 7 0. 05550 8,298. 30.x 30 do do Do. 8 0.05510 4,375 PolyvinylAlcohol Bo1llngHa0 Do. g V 9- 0.04266 756 3,289,2,570 30x30 GelluoseAcetate. Acetone-15 minutes--- Polyethyl'ene/Polyl'sobutylene (50/50);

Polyethylene as surface binder.

The neoprene latex impregnating composition was prepared by adding thevulcanizing dispersion and zinc oxide to the neoprene latex,andfheretfter mixing in a blend of the dispersing agent in water. Thiswas mixed for about five minutes, and thereafter the black pigment wasadded and mixing was carried out for one hour. The dispersing agent andblack pigment were dissolved in 650 parts of water.

Twelve non-woven mats of polyhexamethylene adipamide fibers (2%" inlength and 3 denier/filament) were composited and sprayed on bothsurfaces with the neoprene latex composition, and the surface of thecomposite was sprayed with an additional quantity (about 4.9 parts byweight of the total composition). Before spraying the top web withadditional latex, the weight ratio of binder polymer (neoprene) tofibers was about 60:40. On the top layer was placed a non-woven mat offibers of polyvinyl alcohol (2" in length and 3 denier/filament). Theresulting composite was consolidated at a temperature of 180 C. and1,250 p. s. i. pressure for minutes. Subsequently, the consolidatedsheet was stretched 40% in both directions, and thereafter the solublepolyvinyl alcohol fibers in the upper surface stratum were extracted byimmersing the sheet in hot water for 10 minutes. The resulting sheet wasporous, and the surface stratum contained no structural fibers. Theaverage LPV of several samples of this composition was in theneighborhood of 1,800 grams/ 100 sq. meters/hour, and the sheet was0.0447" in thickness. The fiber-free surface was capable of beingabraded or scuifed with an ink eraser without fuzzing.

EXAMPLE 13 A terpolymer of beta-methoxyethylacrylate/omegachloroethoxyethyl acrylate/ acrylic acid was cast from asolvent solution upon a film of a plasticized polyvinyl chloride. Thisbinder combination served as the top binder layer in a compositecomprising alternate layers of polyvinyl chloride binder and non-wovenfibers of polyhexamethylene adipamide (2 /2" in length and 3denier/filament). The top binder layer was the polyvinyl chloride filmcoated with the above terpolymer. The next layer beneath was a non-wovenmat of the nylon fibers; the layer under that was a polyvinyl chloridefilm; and thereafter three more mats of fibers and two more films ofpolyvinyl chloride were superimposed. As the topmost layer, a web ofpolyvinyl alcohol fibers was placed upon the coated polyvinyl chloridebinder. The relative weights of the components were as follows: 9.26parts of nylon fibers, 9.68 parts of polyvinyl chloride binder, 1.98parts of the terpolymer and 1.10 parts of the polyvinyl alcohol fibers.

The composite was consolidated by pressing at 170" C. under a pressureof 350 p. s. i. for minutes. The resulting consolidated sheet wasstretched 40% in both directions and thereafter placed in boiling waterfor minutes to extract the polyvinyl alcohol pore-forming fibers fromthe surface stratum.

EXAMPLE 14 Four individual mats of non-woven nylon fibers(polyhexamethylene-adipamide, 2 /2 in length and 3 denier/ filament)were impregnated with the following neoprene latex and composited. Theimpregnating composition was composed of the following:

Parts Neoprene latex 820 Plasticizer (oil-soluble sulfonic acid of highmolecular weight with a paraflin oil) 59 Commercial dispersing agent 53Sodium silicate 10 The weight ratio of binder polymer to fibers in thiscomposition was approximately 60:40. The binder polymer was solidifiedby immersing the impregnated composite in a 50:50solution of acetic acidand methanol, followed by washing in water and drying at roomtemperature.

The upper surface of the impregnated composition was brushed with ablack paint comprising chlorosulfonated polyethylene, and the coatingwas permitted to dry. On top of the coating were placed two layers ofnon-woven fibrous mats of polyvinyl alcohol fibers, and the compositewas pressed at 140 C. and 500p. s. i. for 15 minutes. The resultingconsolidated sheet was stretched 40% in two directions, and thepolyvinyl alcohol fibers were extracted in hot water. The resultingsheet had a leather-like surface texture, was permeable to water vapor,and resisted fuzzing upon being scuffed.

EXAMPLE 15 Three composited individual layers of nylon non-woven fibers(polyhexamethylene adipamide, 2 /2" in length and 3 denier/filament)were impregnated with a plasticized polyvinyl chloride contained insolution in tetrahydrofuran, and the solvent was permitted to evaporate.A single layer of non-woven fibers of polyvinyl alcohol (2" in lengthand 3 denier/filament) was similarly impregnated with a plasticizedpolyvinyl chloride contained in solution using tetrahydrofuran as thesolvent. The individually impregnated mats were composited so that thepolyvinyl alcohol fibers were contained in the top layer, and thecomposite was consolidated by pressing at 140 C. and 500 p. s. i. for 10minutes. The consolidated sheet was cooled under pressure and thereafterstretched 30% in two directions. The stretched sheet was then immersedin boiling water for one hour to extract the polyvinyl alcoholpore-forming fibers, and the sheet was dried. The parts by weight of theindividual components in the consolidated sheet were as follows: 15.43parts of nylon fibers, 16.27 parts of polyvinyl chloride binder, and1.94 parts of polyvinyl alcohol pore-forming fibers. The resulting sheetwas permeable to water vapor, and the surface containing no structuralfibers was capable of being subjected to 100,000 scufI's beforeappreciable surface fuzzing was apparent.

EXAMPLE 16 Individual carded non-woven webs of polyhexamethyleneadipamide fibers (the Web weighing approximately 2 ounces per squareyard and the fibers being 1 /2" in length and 3 denier/filament) wereindividually impregnated by spraying one side of each web with thefollowing composition:

degree of impregnation was regulated so that the binder polymer, thatis, the polyvinyl chloride, constituted from 45-51%, by weight of thetotal weight of the impregnated we s.

Four of the impregnated webs were composited so that the grains(direction in which the webs were carded) were perpendicular to adjacentlayers. The composite of webs was pressed at 125 C. and 500 p. s. i. forfive minutes.

A topcoating (3 parts by weight per 81" of surface area) was thenapplied to the composited sheet structure, the top coating being sprayedas before, and the composition being the same as given above. Anon-woven web of polyvinyl alcohol fibers (about 4.5 parts by weight per81" of surface area) was laid upon the top coated surface of theconsolidated sheet, and the composite was then pressed again at C. and500 p. s. i. for five minutes.

structure between screens into a bath of boiling water for a periodwithin the range from 2-10 minutes. After drying, the film was stretchedfurther to an extent of 40% in both directions to form a porous leatherreplacement sheet, having a top surface which resisted surface fuzzingupon abrasion. The resulting sheet composition was permeable to air andWater vapor.

I claim:

1. The process of forming non-woven, porous leather replacement fabricswhich comprises associating substantially water vapor-impermeable,relatively extensible, initially thermoplastic, elastomeric, polymericbinder material with a fibrous sheet comprising essentially a nonwovenbase stratum of uniformly dispersed structural fibers of relativelynon-extensible material, and a non woven surface stratum of uniformlydispersed soluble pore-forming fibers and free of structural fibers toform an initial sheet, said pore-forming fibers being soluble in asolvent which is a non-solvent for the structural fibers, said bindermaterial having a softening temperature below the softening temperatureof said fibers; hot-pressing said initial sheet at a temperature abovethe softening temperature of said binder and below the softeningtemperature of said fibers, whereby to form'a compacted substantiallywater vapor-impermeable sheet wherein said fibers are embedded in saidbinder; stretching said compacted sheet 10% to 50% in at least onedirection to form channels substantially contiguous with the structuralfibers distributed uniformly throughout the base stratum; and dissolvingout said pore-forming fibers with a liquid which is a solvent for saidpore-forming fibers and a non-solvent for said structural fibers andsaid binder material, whereby to form a porous, water vapor-permeablesheet of polymeric binder material reinforced with structural fibers andhaving a porous surface stratum free of fibers.

2. The process of claim 1 wherein the weight ratio of binder tostructural fiber is within the range of from 30:70 to 70:30.

3. The process of claim 2 wherein the weight of said pore-forming fibersis within the range of from 5% to 25% of the total weight of fibers insaid sheet.

4. The process of forming non-woven, porous, leather replacement fabricswhich comprises associating initially thermoplastic, elastomeric,polymeric binder material with a fibrous sheet comprising essentially anon-woven base stratum of uniformly dispersed liquid-swellablestructural fibers and a non-woven surface stratum of uniformly dispersedsoluble pore-forming fibers free of structural fibers to form an initialSheet, said pore-forming fibers being soluble in a solvent which is anon-solvent for the structural fibers, said binder material having asoftening temperature below the softening temperature of said fibers,

hot-pressing said initial sheet at a temperature above the softeningtemperature of said binder and below the softening temperature of saidfibers whereby to form a compacted, ubstantially watervapor-impermeable, composite sheet wherein said fibers are embedded insaid binder; soaking said compacted composite sheet at a temperaturebetween the softening temperature of said binder and of said fibers in aliquid which swells the structural fibers; dissolving out saidpore-forming fibers with a liquid which is a solvent for saidpore-forming fibers and a non-solvent for said structural fibers andsaid binder material; and drying the resulting sheet at a temperature nogreater than the softening temperature of the binder polymer to removesaid liquid, whereby to form a porous, water vapor-permeable sheetreinforced with structural fibers and having a porous surface stratumfree of fibers.

5. The process of claim 4 wherein the weight ratio of binder tostructural fiber is within the range of from 30:70 to 70:30.

6. The process of claim 5 wherein the weight of said pore-forming fibersis within the range of from 5% to 25% of the total weight of fibers insaid sheet.

7. A porous, water vapor-permeable leather replacement materialcomprising a sheet of initially thermoplastic, elastomerie, polymericbinder material having an integral porous surface stratum free offibers; the remaining cross-section of the sheet being watervapor-permeable and having reinforcing structural fibers uniformlydistributed throughout, the water vapor-permeability in said remainingcross-section being contributed solely by channels substantiallycontiguous with the structural fibers.

8. The product of claim 7 wherein the binder material of said surfacestratum is different from the binder material of said remainingcross-section.

9. The product of claim 7 wherein the weight ratio of binder material tostructural fibers is within the range of from 30:70 to 70:30.

10. The product of claim 7 wherein the weight of said binder materialcomprises from 40% to of the total weight of binder and fibers.

11. The product of claim 7 wherein the structural fibers are at least0.01 of an inch in length.

12. The product of claim 7 wherein the structural fibers are about 1.5inches in length.

References Cited in the file of this patent UNITED STATES PATENTS2,474,201 Raymond t al. June 21, 1949 2,650,184 Biefeld Apr. 25, 19532,676,128 Piccard Apr. 20, 1954

1. THE PROCESS OF FORMING NON-WOVEN, POROUS LEATHER REPLACEMENT FABRICSWHICH COMPRISES ASSOCIATING SUBSTANTIALLY WATER VAPOR-IMPERMEABLE,RELATIVELY EXTENSIBLE, INITIALLY THERMOPLASTIC, ELASTOMERIC, POLYMERICBINDER MATERIAL WITH A FIBROUS SHEET COMPRISING ESSENTIALLY A NONWOVENBASE STRATUM OF UNIFORMLY DISPERSED STRUCTURAL FIBERS OF RELATIVELYNON-EXTENDIBLE MATERIAL, AND A NONWOVEN SURFACE STRATUM OF UNIFORMLYDISPERSED SOLUBLE PORE-FORMING FIBERS AND FREE OF STRUCTURAL FIBERS TOFORM AN INITIAL SHEET, SAID PORE-FORMING FIBERS BEING SOLUBLE IN ASOLVENT WHICH IS A NON-SOLVENT FOR THE STRUCTURAL FIBERS, SAID BINDERMATERIAL HAVING A SOFTENING TEMPERATURE BELOW THE SOFTENING TEMPERATUREOF SAID FIBERS; HOT-PRESSING SAID INITIAL SHEET AT A TEMPERATURE ABOVETHE SOFTENING TEMPERATURE OF SAID BINDER AND BELOW THE SOFTENINGTEMPERA-